This invention relates generally to agricultural balers and, in particular, to knotter trip mechanisms for such balers.
In a conventional type of baler, a plunger reciprocates in a bale case to form crop material into rectangular bales. Tying mechanisms comprising needles and knotters are provided to tie several strands of binding material such as twine around the bales, and a trip mechanism is employed for automatically actuating the knotters when bales reach a desired length. Such trip mechanisms are disclosed in U.S. Pat. No. 2,897,748 and British application 1,169,137.
Conventionally, the knotter drive shaft controlling the operation of both the needles and the knotter mechanisms is rotated at the same rotational speed as the plunger crank arm so that the knot tying cycle is completed only when the plunger is retracting, or while the bale, which previously has been compressed in the bale chamber, is springing back thereby resulting in the bale being of relatively low density as it exits from the bale chamber. This characteristic causes low energy efficiency as crop material has to be compressed much harder to obtain a given density in the finished bale. This characteristic also may cause problems with the knot tying operation as knots may not hold firmly after completion.
Although these problems are not critical in conventional, small rectangular balers which produce bales typically weighing in the range of 20 to 30 kg, the situation is different with medium and large rectangular balers which produce bales weighing in the range of 200 up to 1000 kg. In such medium and large square balers, the problems described above that are caused by the bales expanding in the bale case prior to the knotting cycles being completed are much more noticeable. The springing back of crop material prior to the knotting cycle being completed is much more significant causing bales of relatively low density and resulting in power inefficiency. Also, the knot tying operation is often adversely affected resulting in frequent misties.
It has already been proposed in the art, as disclosed in German patent 1,095,044, to rotate the tying mechanism drive shaft at twice the rotational speed of the plunger crank arm. Others also have already proposed, as disclosed in German patent 804,616, to rotate the tying mechanism main shaft through only one half or one third of a complete revolution during the tying cycle. With both of these proposals, the tying operation is completed in less than one complete reciprocating cycle of the plunger thereby greatly reducing the above-described problems. However, these proposals have caused another problem which is concerned with timing the operation of the tying mechanism with the plunger movement. In conventional hay balers, the knotter drive shaft is rotated at the same rotational speed as the plunger crank arm when the knotter trip mechanism is tripped. Therefore, timing the knotter operation with the plunger movement is very simple. As is generally known in the art, the knotter trip mechanism is operable to always trip the knotter cycle at precisely the same point in the plunger cycle. Incorrect timing between the plunger movement and the knotting cycle would disturb and make the knotter operation ineffective. Unless special precautions are taken, such incorrect timing easily could occur in arrangements where the tying cycle is completed in less than a full reciprocating cycle of the plunger.
U.S. Pat. No. 4,503,762 discloses means for timing the tying cycle with the movement of the plunger in the direction to compress crop material in the bale case. A tying mechanism is provided with a drive line including a clutch mechanism having a pawl assembly, the position of which is controlled by a first trip mechanism coupled to a bale length metering apparatus. In addition, a second trip mechanism is cooperable with the pawl assembly and operatively associated with the baler plunger in a manner such that the pawl assembly, when tripped by the first trip mechanism to a drive engaging position, is returned to its drive interrupting position when the plunger is retracting in the bale case. The second trip mechanism, however, is continuously oscillated between a pawl assembly holding position and a pawl assembly releasing position during the entire bale compressing cycle preceding the tying cycle of the formed bale. This manner of operation is very inefficient considering that the second trip mechanism only has to interfere once in a complete bale forming cycle, and more specifically, during the tripping of the tying mechanism. Unnecessary wear of the components of the second trip mechanism results therefrom, requiring increased maintenance. Furthermore, the structure operatively connecting the baler plunger to the second trip mechanism is located close to the plunger compressing area where the structure is subjected to dirt and crop resulting in abrasion and possible lack of operation. The second trip mechanism is positioned such that, upon the first trip mechanism being tripped, it cannot prevent an initial coupling between the tying mechanism and its drive line. Such an initial coupling is prevented after a short angular displacement of the tying mechanism drive shaft provided the baler plunger is retracting in the bale case. Accordingly, energy is lost in setting the tying mechanism in motion for a small initial displacement. This initial displacement results in the tying mechanism being removed from its optimum start position thereby causing high inertia forces when it is actuated a second time to complete the tying cycle.